<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
<head>
<title>star</title>
<script type="text/javascript">
window.onload = function () {
C = Math.cos; // cache Math objects
S = Math.sin;
U = 0;
w = window;
j = document;
d = j.getElementById("c");
c = d.getContext("2d");
W = d.width = w.innerWidth;
H = d.height = w.innerHeight;
c.fillRect(0, 0, W, H); // resize <canvas> and draw black rect (default)
c.globalCompositeOperation = "lighter";  // switch to additive color application
c.lineWidth = 0.2;
c.lineCap = "round";
var bool = 0, 
t = 0; // theta
d.onmousemove = function (e) {
if(window.T) {
if(D==9) { D=Math.random()*15; f(1); }
clearTimeout(T);
}
X = e.pageX; // grab mouse pixel coords
Y = e.pageY;
a=0; // previous coord.x
b=0; // previous coord.y 
A = X, // original coord.x
B = Y; // original coord.y
R=(e.pageX/W * 999>>0)/999;
r=(e.pageY/H * 999>>0)/999;
U=e.pageX/H * 360 >>0;
D=9;
g = 360 * Math.PI / 180;
T = setInterval(f = function (e) { // start looping spectrum
c.save();
c.globalCompositeOperation = "source-over"; // switch to additive color application
if(e!=1) {
c.fillStyle = "rgba(0,0,0,0.02)";
c.fillRect(0, 0, W, H); // resize <canvas> and draw black rect (default)
}
c.restore();
i = 25; while(i --) {
c.beginPath();
if(D > 450 || bool) { // decrease diameter
if(!bool) { // has hit maximum
bool = 1;
}
if(D < 0.1) { // has hit minimum
bool = 0;
}
t -= g; // decrease theta
D -= 0.1; // decrease size
}
if(!bool) {
t += g; // increase theta
D += 0.1; // increase size
}
q = (R / r - 1) * t; // create hypotrochoid from current mouse position, and setup variables (see: http://en.wikipedia.org/wiki/Hypotrochoid)
x = (R - r) * C(t) + D * C(q) + (A + (X - A) * (i / 25)) + (r - R); // center on xy coords
y = (R - r) * S(t) - D * S(q) + (B + (Y - B) * (i / 25));
if (a) { // draw once two points are set
c.moveTo(a, b);
c.lineTo(x, y)
}
c.strokeStyle = "hsla(" + (U % 360) + ",100%,50%,0.75)"; // draw rainbow hypotrochoid
c.stroke();
a = x; // set previous coord.x
b = y; // set previous coord.y
}
U -= 0.5; // increment hue
A = X; // set original coord.x
B = Y; // set original coord.y
}, 16);
}
j.onkeydown = function(e) { a=b=0; R += 0.05 }
d.onmousemove({pageX:300, pageY:290})
}


</script>
</head>

<body style="margin:0px;padding:0px;width:100%;height:100%;overflow:hidden;">
<canvas id="c"></canvas>
</body>
</html>